This invention relates to the dyeing of synthetic fibers which have been modified chemically to make them receptive to basic cationic dyestuffs, especially fibres of polyacrylonitrile containing 85% or less acrylonitrile units, polyesters and polyamides.
Synthetic fibers have such a strong affinity for basic dyestuffs that the dyes, which become absorbed on the dye sites, do not distribute themselves uniformly under atmospheric dyeing conditions at the boil. This results in uneven or unlevel dyeing. In the dyeing of acrylics, the affinity of each dye and the rate of exhaustion of dyestuffs from the dyebath vary with the dye being used often making the levelness of dyeing unpredictable. Temperature differences from one part of the dyeing equipment to the other aggravate this difficulty. Certain chemical additives and methods have been used to overcome these difficulties to a certain extent, but there are still deficiencies in performance, handling and cost which make them unacceptable for routine dyeing.
In an attempt to increase the absorption and improve the evenness of the dyeings, certain substances generally referred to as dyeing assistants are added to the dye bath to promote or to control dyeing. Such substances aid in the achievement of uniform absorption of the dye by the fiber. The manner in which the level-dyeing is accomplished depends generally upon the particular dyestuff in use and also upon the substance which is employed as a dyeing assistant. Usually, a dyeing assistant will aid in promoting level deposition of the dye on the fiber or fabric in several ways. Some dyeing assistants will accomplish the desired result by delaying the absorption of the dye by the fiber. Anionic dyeing assistants will function as such by accelerating the dye absorption on the material to be colored. However, in many cases, it has been found that the addition compounds formed between the dyestuff and the aforesaid dyeing assistants are very stable and in the course of the dyeing process, the dyestuff is only partially liberated even if the temperature is increased. As a result, considerable amounts of dyestuffs are lost during the dyeing process.
In an attempt to avoid the aforesaid difficulties with respect to dyeing, retarders have been employed to cause the rate of strike to become slower at the critical temperature that is, at the temperature between 180.degree. and 200.degree. F. Two types of retarders have been generally used; the first type is the cationic retarder and a substance of this type functions by competing with the dye for the available dye sites. A cationic retarder has more affinity for the dye site and, due to its smaller molecular size, is able to precede the dye at slightly lower temperatures. As a result, less dye sites are available at temperatures between about 180.degree. and 200.degree. F. and the shortage of sites causes the dye to seek out vacant sites and draw out of the bath evenly. It has been shown that with this retarder system, the dye strike from the 200.degree.-206.degree. F. is extremely rapid and this further narrows an already dangerously narrow temperature range.
In order to dye synthetic fibers by the exhaustion method with basic dyestuffs and in level shades, a dye liquor has been used which in addition to basic dyestuffs, contained as dye assistants tertiary, mono- or bis-quaternary organic nitrogen compounds having at least one higher alkyl radical per molecule. As a rule, these assistants detrimentally affect the fastness to light of the dyeings obtained and block the fibers i.e., as soon as a portion thereof has been drawn onto the fiber, they reduce the absorption power of the fiber both for further basic dyestuff and for further dye assistant. This blocking effect on the fiber makes the redyeing and in particular cross dyeing of a shade already attained very much more difficult. Since the blocking effect caused by the known dye assistants on the polyacrylonitrile fiber affects the individual basic dyestuff present in a mixture of dyes in different degrees, it is also often impossible to attain or reproduce a desired shade with mixtures of basic dyestuffs. Finally, the blocking effect has a varying influence on the rate at which the basic dyestuffs draw onto the aforesaid type of fibers which, in practice, leads to uneven distributions of the dyestuffs. Moreover, since the hitherto used dye assistants which have drawn onto the fiber are very difficult to remove, this blocking effect is often irreversible.
In the prior art many methods for obtaining level cationic dyeings are described in the literature for instance in the U.S. Pat. Nos. 3,667,899 3,632,300 and 3,355,243. The object of this invention is to obtain well-penetrated level dyeings and maximum color yield with cationic dyestuffs. This objective is achieved by using cationic surface active agents having the following general structure: ##STR2##